The present invention relates to plural component mixing and dispensing systems, and more particularly to a system and method of operation for producing zero waste of the liquid components fed to the system.
Plural component liquids are typically liquids which are chemically inert in their respective individual states, and chemically reactive when brought together and mixed to form a composite liquid mixture. In the chemically active state, such mixed liquids, commonly comprising a resin component and a catalyst component, are characterized in that they require only a short time interval to become "set" or to solidify. Once such liquids have become solidified they are capable of providing advantageous coatings in the coating materials field, or other advantageous chemical and physical behavior in other fields, depending upon the nature and type of materials being used. For example, such materials are used to provide extremely durable finishes on metals and other materials, they are also used to provide foam insulation for construction projects, and they are also used to provide unique filling and packing materials for furniture, packaging, and other purposes. Because such materials are chemically active when mixed together, they do present a significant problem in handling, particularly when they are utilized in a system which requires intermittent application. Once the materials become mixed together, they must be specially handled during the limited time in which they remain in a relatively fluid state, for once they solidify it is practically impossible to return them to a liquid or fluid state.
In systems for mixing and dispensing such materials, it has been a continual problem to provide application procedures and equipment which do not waste at least some material, particularly during intermittent dispensing operations. The mixing of the two materials must occur prior to the point where they are dispensed, and after the dispensing operation is completed there is therefore always some quantity of mixed material remaining in the dispensing mechanism which must be disposed of. In most cases this material is purged from the system into a waste collector by utilizing solvents as a purging and cleaning solution. This necessitates the need for waste collection containers, and requires that suitable storage and disposal procedures be adopted.
It has been found, that for at least certain types of resin and catalyst components, the setting time for conversion of mixed components into solids is a direct function of the mix ratio of these components. It has been found further that the ratio can be diluted to such an extent to retard the setting time to a time interval considerably longer than the intermittent "off" time of the system when used in such intermittent applications. For example, in a typical plant environment, such application systems may be utilized relatively continuously during the work day, but may then be unused during one or several work shifts when the plant is either closed down, or when other operations are performed not requiring the dispensing of these components. Formerly, this situation would require that the system be completely purged of mixed components and thoroughly cleaned before shutdown, and at the time the system is restarted the system would be again refilled with properly mixed materials to enable the start up of a new dispensing operation.